ORIGINAL RESEARCH Plasma Confinement Modification in IR-T1 Tokamak by Velocity Shear Stabilization M. Ghoranneviss • M. Lafouti • S. Meshkani • A. Salar Elahi Published online: 13 December 2013 Ó Springer Science+Business Media New York 2013 Abstract E 9 B velocity shear effects on the plasma confinement were investigated in the IR-T1 tokamak. The investigations have been done at the presence of external applied electric and Resonant Helical magnetic Fields (RHF). In this work, experimental data have been mea- sured by using two arrays of the Langmuir probes in both the radial and poloidal directions. A velocity shear stabil- ization mechanism has also been proposed to be respon- sible for an improvement in plasma confinement. The results show that E r 9 B drift velocity (V E9B ) reduces about 90 % due to applied biasing and RHF at edge plasma. We have also observed that positive biasing and RHF lead to a significant decrease ( [ 80 %) for radial turbulent transport (C E9B ) at edge plasma. In this paper, the electrostatic Reynolds stress (Rs) and the shearing rate c E9B have been calculated. We have also compared the Rs and c E9B at presence of the biasing and RHF and without biasing and RHF. A good correlation between confinement modifications and E r 9 B velocity shear has been found suggesting that confinement enhancement originates at the edge plasma as a consequence of the formation of a particle transport barrier just inside the limiter. Keywords Tokamak  Drift velocity  Turbulent transport Introduction The understanding and reduction of turbulent transport in magnetic confinement devices is not only an academic task, but also a matter of practical interest, since high confinement is chosen as the regime for ITER and possible future reactors since it reduces size and cost. The interplay of radial electric field (E r ) and plasma confinement in toroidal devices has been a subject of theoretical and experimental study since the very beginning of tokamak research [1]. Many papers have been devoted to the effect of electric field biasing in specific machines, which in general leads to a strongly varying radial electric field as a function of radius and a resulting sheared E 9 B flow, giving rise to improved confinement properties. The importance of radial electric fields for plasma transport was in the past repeatedly established. Since the discovery of the transition from a low confinement mode (L-mode) to a high confinement mode (H-mode) in 1982 [2], a flurry of activity started with the experimental and theoretical rec- ognition of a link between E r and the formation of edge and internal transport barriers in toroidal plasmas. The impor- tance of radial electric field shear in the L–H transition was suggested for the first time in [3, 4]. The (spontaneous) H-mode has been obtained in a variety of tokamaks mainly with elongated plasma cross section and divertor, and recently also in the limiter tokamak T-10 with ECRH as the only auxiliary heating. An (induced) H-mode can also be triggered externally by imposing an electric field and the resulting E 0 B rotation in tokamaks like TEXTOR, CAS- TOR, T-10 and ISSTOK, as well as in reversed field pin- ches like RFX. These electrode biasing experiments have contributed significantly to the understanding of the H-mode phenomenon and of the effects of E r on plasma transport. The L–H transition is accompanied by a M. Ghoranneviss  M. Lafouti  S. Meshkani  A. Salar Elahi (&) Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran e-mail: Salari_phy@yahoo.com 123 J Fusion Energ (2014) 33:158–165 DOI 10.1007/s10894-013-9653-6